Optical Thomson scattering measurements of cylindrical wire array parameters

Abstract

A Thomson scattering diagnostic has been used to measure the parameters of cylindrical wire array Z pinch plasmas. The scattering operates in the collective regime (α>1) allowing spatially localised measurements of the ion or electron plasma temperatures and of the plasma bulk velocity. The ablation flow is found to accelerate towards the axis reaching peak velocities of 1.2–1.3 × 107 cm/s in aluminium and ∼1 × 107 cm/s in tungsten arrays. Measurements of the precursor ion temperature shortly after formation are found to correspond to the kinetic energy of the converging ablation flow. Measurements during the implosion phase of tungsten arrays show the main imploding mass reaches velocities of ∼1.4–1.7 × 107 cm/s and is non-zero even at large radii close to the start of the x-ray pulse indicating current flow in the trailing mass.

Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches

“…The estimated range was M 1 ¼ 6.2!9.2. Combining this estimate with previously published measurements of the flow velocity taken from Thomson-Scattering experiments 28 allowed us to estimate a range for the ZT e of the plasma, 13-89 eV. These ranges make no assumptions about the value of c for the plasma, however, earlier calculations using an ionising plasma model 23 allowed us to estimate a smaller range for this parameter, c $ 1.09-1.13.…”

“…Fig. 8 shows plots of the radial velocity profiles measured for both 16 and 32 wire aluminium arrays taken from a paper by Harvey-Thompson et al 28 In these experiments, the Thomson scattering beam was aligned through a pair of opposing inter-wire gaps, such that the velocities measured for the 32 wire arrays should correspond directly to the flow velocity in the primary shock region, the same region for which we have calculated the Mach number. The range of radii over which our determination of the Mach number is relevant is r$3-5 mm.…”

“…III B), can be used in combination with recently published flow velocity measurements from Thomson scattering experiments 27,28 to further investigate the parameters of the aluminium ablation plasma. Fig.…”

Shock-less interactions of ablation streams in tungsten wire array z-pinches

“…The electron temperature of the ablation streams has been measured using Thomson scattering in only a very limited number of experiments, and in those cases the lack of spectral resolution meant that the results could only be treated as upper limits for this parameter, ZT e < 100 eV. 18 For our calculations, we relied on the results of MHD simulations using the GORGON code, which indicate that temperatures in these ablation flows should be around T e $ 10-20 eV. 27 Calculations of the slowing down MFP were carried out over a range of plasma parameters.…”

“…These results are then discussed with reference to previously published Thomson scattering measurements of the plasma conditions in these arrays. 17,18 …”